the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 05 Nov 2024
Measurement report: Crustal materials play an increasing role in elevating particle pH: Insights from 12-year records in a typical inland city of China
Abstract. Particle acidity is a critical parameter that affects atmospheric chemistry. Concerns have been raised about the exacerbating aerosol and rainfall acidity due to China’s ongoing efforts to reduce ammonia emissions. Therefore, it is urgent to clarify the changing trends in particle pH response to air pollution control policies, especially in North China, which is significantly affected by dust aerosol. 12-years observational data in Zhengzhou reveal that the annual average PM2.5 concentration decreased from 212 ± 102 μg/m3 in 2013 to 60 ± 41 μg/m3 in 2022, with the largest reduction in sulfate (79 %). Correspondingly, the annual particle pH increased by 0.11 units from 2013 to 2019. In addition, the elevated particle pH in 2015 and 2018 was notably influenced by the increase in TNHx (NH3 + NH4+). Note that the crustal material concentrations and their proportions increased significantly during 2019–2022, which might be responsible for the resuspension of surrounding soil dust. Even though the TNHx concentration was decreasing, the annual average growth rate of pH values increased to 0.21 units from 2019 to 2022. This phenomenon is not unique to Zhengzhou, as major cities in the North China Plain have also experienced a pronounced upward trend in coarse particles after 2019. Therefore, the future ammonia reduction policies in North China may not lead to a rapid increase in particle acidity buffering by the crustal materials.
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RC1: 'Comment on egusphere-2024-2869', Anonymous Referee #1, 03 Dec 2024
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In this article, the authors analyze 12 years of field observation data from Zhengzhou, China, to investigate trends in aerosol composition concentrations and its acidity. This approach is well-aligned with the scope and objectives of the “Measurement Report”, making the study highly relevant. However, there are contentious aspects in the discussion and final conclusions of this article. Specifically, whether crustal materials play a dominant role in driving the changes in aerosol acidity remains uncertain. This issue affects several parts of the article, including its main argument and even the title. I believe the authors are capable of making substantial revisions to the article.
Here are my specific recommendations:
Lines 15-17: Compared to the reduction of ammonia emissions, the reductions in acidic precursors such as SO2 and NOx have been more significant, leading to an overall increase in atmospheric acidity (including aerosols, clouds, and precipitation). Studying the trends in aerosol acidity is highly meaningful, but it is essential to consider the combined impact of the reduction in both acidic and basic precursors.
Lines 19-21: The 12-year observation period and the corresponding years for the PM concentration results do not align. While I understand that the authors began observations in 2011, the abstract should be rephrased to ensure clarity and consistency in the presentation of the time frame.
Lines 28-29: According to mainstream forecasts regarding the need for further PM reduction under China’s carbon peaking and carbon neutrality policy, future emission reduction strategies will primarily focus on acidic precursors. The expression here needs to be more precise and cautious.
Lines 63-65: There is a lack of logical flow from the previous discussion of acidity changes to the conclusion/summary in this sentence. Additionally, aerosol acidity is unlikely to be neutral or even approach neutrality by nature in general.
Lines 66-67: This may not be entirely accurate. The relative contribution of sulfate and nitrate does not directly determine aerosol acidity. The authors need to identify the true driving factors behind the pH trend. In my opinion, the main drivers are the NH3/NH4+ multiphase buffering, ALWC, and non-volatile cations, rather than other components or temperature. This is because, over the long term, the impact of temperature variations on pH is minimal within the same season.
Lines 85-86: Given the limitations, under what circumstances does it go from 4 to 7?
Lines 93-94: After reviewing the research progress, I suggest concluding with a summary that introduces the focus of this article. Specifically, what makes Zhengzhou and other cities different, what issue this study aims to address based on previous research, and what contributions this study makes. This is essential in scientific writing.
Line 123: Provide the version of ISORROPIA and the time resolution of the input components.
Line 160: The spring of 2021 saw multiple rare dust storms in the North China Plain, but why was the CM not high in 2021? Additionally, the resolution of the figures in both the main text and SI needs to be improved to at least 300 dpi, as many figures in the SI are unclear.
Line 170 (Figure S3): It is recommended to use the same y-axis range for consistency. Regarding the drivers of seasonal variations (increase or decrease), I believe the discussion here lacks sufficient rigor, with an incomplete chain of evidence. I suggest that the authors consider separately discussing natural and anthropogenic sources, especially the impact of spring dust storm events on dust levels. In section 3.3, the source-related discussion is also mentioned, and therefore, this part needs to be strengthened.
Lines 239-241: I believe ALWC is an important factor influencing pH, and it should not be solely attributed to sulfate. The authors need to carefully consider this point. Specifically, it should be evaluated whether the continuous decrease in ALWC affects pH, and whether this impact might even outweigh the influence of changes in aerosol composition.
Lines 280-282: Where is the data for this section sourced from?
Lines 283-286: Although many researchers have done significant work on the impact of ammonia reduction on PM levels, I believe that under China’s current policies, future emission reductions will not primarily focus on ammonia. Therefore, the authors need to reconsider whether the focus of this "Measurement Report" should be placed on ammonia. I suggest that the authors revise all statements related to ammonia, including the title.
Citation: https://doi.org/10.5194/egusphere-2024-2869-RC1
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Measurement report: Crustal materials play an increasing role in elevating particle pH: Insights from 12-year records in a typical inland city of China-Data H. Zhang https://doi.org/10.5281/zenodo.14032007
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